1. Field of the Invention
The present invention relates to hardware configurations of communication apparatuses (at the base station and terminals) employing communication method using an interleaving or de-interleaving efficiency in the processes of modulation and demodulation. The invention is particularly advantageous for communication apparatuses for mobile communication supporting a code division multiple access (CDMA) protocol.
2. Description of Related Art
Interleaving is a technique for transmitting data in a way less susceptible to errors occurring in a burst manner on a transmission path by rearranging the data in a prescribed pattern. It is extensively used in a wide variety of communications, such as mobile communication and Internet communication.
Standards developed under the Third Generation Partnership Project (“3GPP”), an international standardization body for mobile communication systems supporting a wide band code division multiple access (W-CDMA) protocol, also apply the interleaving technique. FIG. 1 illustrates a RAM configuration based on the 3GPP according to the prior art, and FIG. 2 is a conceptual diagram of the interleaving technique which illustrates the effect of error correction.
The interleaving processing according to the 3GPP standard is characteristic in that, while the usual transmission frame unit is 10 ms, data are rearranged in a long period up to 80 ms. To rearrange their transmitting sequence, data delivered from their origin are spooled in a RAM area 001. When they are written into the RAM area 001, the address is incremented in the usual order of 1, 2, 3, etc. Data are written in every 30 of each line as shown in FIG. 2. When an 80 ms equivalent length of data have accumulated, the read sequence is varied to 1, 31, 61 etc., i.e., the data are read out at the interval of 30 (by row) then copied into another RAM area 002. The sequence of the columns to be read is varied at random with reference to a prescribed pattern.
The transmission of data in such a rearranged sequence makes it easier for the error correction code to exert its effect. Even if many errors are locally generated by noise or the like on the transmission path as shown in FIG. 2, the rearrangement of the data into the original sequence on the receiving side (which is known as de-interleaving) disperses the error locations. For instance, where a convolutional code of a ⅓ rate is used, information of each original datum is stretched to three data, and accordingly if all the three become erroneous, no decoding will be possible. But if only one of the three runs into an error, restoration can be done with high accuracy.